A side-looking radar has one or two antennas which are pointed in a direction perpendicular to the aircraft axis and it emits pulses which sweep the ground. The return echoes contain data concerning the ground; the better the system resolution, the better the ground image which can be produced. In the direction perpendicular to the aircraft axis, a fine transverse resolution is obtained by the emission of short pulses using, for example, the technique called "pulse compression". In the direction of the aircraft movement, an equivalent resolution can be obtained only by suitable processing of the video signal delivered by the radar receiver.
Among the processing devices known in the art, those which use a correlation procedure are the only ones at present allowing a sufficiently fine resolution to be obtained. However, processing must be done on the gorund because of the complexity and volume of the equipment which cannot be airborne.
Existing devices use either an optical correlation procedure, which requires the video signal to be recorded on a photosensitive base, to be developed and processed in coherent light by equipment which is not only highly sophisticated but also costly, fragile and cumbersome, or a digital correlation process using an actual computer which receives the data recorded in flight and coded. In neither case can processing be carried out in real time, nor can the image of the terrain explored be presented to the pilot or used immediately on board the aircraft in flight.